1. Field of the Invention
The present invention relates to a rotation detecting device for detecting the number of revolutions of a rotating element such as a wheel and for transmitting wireless an electric signal indicative of the detected number of revolutions. The present invention also relates to a wheel support bearing assembly utilizing the rotation detecting device referred to above and to a rolling bearing assembly equipped with an electric power generator that provides an electric power source or the like for the rotation detecting device of the type referred to above. The rolling bearing assembly equipped with the electric power generator can find a variety of applications such as in a wheel support bearing assembly provided with a wireless sensor and an ABS system.
2. Description of the Prior Art
A rotation detecting device for detecting the number of revolutions, or the rotational speed for short, that is equipped with an electric power generator and a wireless transmission unit has been well known in which the electric power generator includes a magnetic ring assembly accommodating a coil and a multi-pole magnet assembly. In this electric power generator employed in the known rotation detecting device, the magnetic ring assembly is mounted fixedly on one of rotatable and non-rotatable members while the multi-pole magnet assembly is mounted fixedly on the other of the rotatable and non-rotatable members, so that a relative rotation of those rotatable and non-rotatable members can result in generation of an electric power. An output signal indicative of the rotational speed, which is generated from the electric power generator, is transmitted wireless by the wireless transmission unit.
The electric power generator referred to above is disposed between pluralities of raceways defined in the non-rotatable and rotatable members, respectively, with the multi-pole magnet assembly and the magnetic ring assembly disposed between the pluralities of such raceways. Also, a sealing member for sealing a working space delimited between the non-rotatable and rotatable members is integrated together with the multi-pole magnet assembly, while the structure may also be available in which the multi-pole magnet assembly and the magnetic ring assembly are positioned externally of the seals.
In the electric power generator in which the multi-pole magnet assembly and the magnetic ring assembly are disposed externally of the seals, the multi-pole magnet assembly is exposed to foreign matter such as saline dirt and grits and, therefore, an anti-rusting treatment is required where the multi-pole magnet assembly makes use of magnets such as rare-earth magnets that are susceptible to rusting. Also, where the magnetic ring assembly is also susceptible to saline dirt and grits, the anti-rusting treatment has to be applied to the magnetic ring assembly. The anti-rusting treatment to be applied to the magnets and the magnetic ring assembly includes a plating process, in which zinc or nickel is plated on surfaces of the magnets and the magnetic ring assembly, a painting process in which an anti-rusting paint is applied to surfaces of the magnets and the magnetic ring assembly, and a resin molding process in which the magnets and the magnetic ring assembly are covered with a resin material.
When the anti-rusting treatment against the saline dirt and grits is employed, the plated or painted layer must have a relatively large film thickness. In particular, where the resin molding process is used, the resultant resin layer has a film thickness generally greater than the plated or painted layer. Accordingly, if the anti-rusting treatment is applied to the magnets and the magnetic ring assembly, particularly to respective surfaces of the magnetic ring assembly and the magnets that confront with each other, a gap between the magnets and the magnetic ring assembly would undesirably increase enough to lower the electric power output generated by the electric power generator. Although the problem associated with reduction in electric power output of the electric power generator would be resolved if the number of turns of the coil accommodated in the magnetic ring assembly is increased and/or the magnets of a relatively large thickness are employed, any of those measures would result in an undesirable increase of the size of the electric power generator.
Also, if foreign matter enter between the respective surfaces of the magnetic ring assembly and the magnets that confront with each other, those surfaces would be scratched or otherwise damaged in contact with the foreign matter and the anti-rusting film or mold would then be impaired enough to allow rusting to occur in those surfaces. Because of this, additional seals would be required to avoid ingress of the foreign matter.
One example of the rolling bearing assembly equipped with the electric power generator of the kind discussed above is currently available and is shown in FIG. 38A. Referring to FIG. 38A, the rolling bearing assembly 71 includes an inner race 72 defining the non-rotatable member and an outer race 73 defining the rotatable member. An electric power generator 76 used therein includes a stator 74, i.e., a magnetic ring assembly mounted on one end of the inner race 72, and a rotor 75, i.e., a multi-pole magnet assembly mounted on an adjacent end of the outer race 73, and generates a rotational speed detection signal indicative of the number of revolutions of the outer race 73 in terms of the electric power generated thereby. In such structure, an electric circuit unit 77 is provided at a location outwardly of one end of the inner race 72 defining the non-rotatable member, so as to extend axially outwardly from the position where the multi-pole magnet assembly 75 is disposed. In the example now under discussion, this electric circuit unit 77 includes an electric circuit substrate 79 encased within, for example, a metallic protective casing 78 as shown in FIG. 38B and having various electric component parts necessary to form a signal processing circuit, an electric power source circuit, a transmission circuit and others. The coil 80 in the magnetic ring assembly 74 and the electric circuit unit 77 are electrically connected with each other by means of an electric wiring 81. According to the conventional example shown in FIGS. 38A and 38B, the electric power generated by the electric power generator 76 is utilized not only as the rotational speed detection signal, but also as an electric power source for electrically powering the signal processing circuit and the transmission circuit through an electric power source circuit, and the rotational speed detection signal is subsequently transmitted wireless from a transmitting antenna 82 of the transmission circuit to an external receiver circuit.
However, with the above discussed conventional rolling bearing assembly of the type equipped with the electric power generator, the electric circuit unit 77 including the electric power source circuit, the processing circuit for processing the rotational speed detection signal, the transmission circuit and others is necessarily disposed at a location distant and separate from the electric power generator 76, hence involving a problem associated with complication in structure. Also, a complicated procedure is required to electrically connect the coil 80 in the magnetic ring assembly 74 and the electric circuit unit 77 together through the electric wiring 81. Considering that the coil 80 makes use of a relatively thin electric wire, a terminal treatment is required to lead the electric wire out from the coil 80, resulting a substantial amount of manual intervention. In addition, a measure to avoid any possible breakage of joints in the electric wiring 81 and a protective casing 78 for protecting the electric circuit unit 77 from external environment are needed and does therefore provide a cumbersome addition to the complicated structure and the complicated assemblage.
Furthermore, an anti-skid braking system (ABS) is known, which operates to detect the onset of a wheel skid, which would be likely to occur when the wheel rotates on a low friction ground surface or is abruptly braked, and then to loosen the braking to thereby maintain tire grip to secure a steering control. A rotational speed sensor for detecting the onset of the wheel skid is generally disposed in the wheel support bearing assembly. This sensor has a sensing portion disposed in face-to-face relation with a pulsar ring mounted on, for example, one end of a raceway member positioned externally of the bearing assembly. However, since the pulser ring and the sensing portion are exposed to the outside, a problem would often occur in that reduction in size of the wheel support bearing assembly tends to be hampered. In order to alleviate such problem, wheel support bearing assemblies have been suggested in which an electric power generator that serves as a rotational speed sensor for providing an output signal indicative of the number of revolutions of the wheel is employed and in which, as shown in FIG. 39, arrangement is made to transmit the rotational speed detection signal wireless.
Referring now to FIG. 39, the wheel support bearing assembly shown therein makes use of an electric power generator 86 of a structure in which a multi-pole magnet assembly 85 is mounted on an inner member 82 of the bearing assembly and a magnetic ring assembly 84 is mounted on an outer member 83 so as to confront the multi-pole magnet assembly 85 in a direction radially of the bearing assembly, so that a relative rotation between the inner and outer members 82 and 83 can result in generation of an electric power. The inner member 82 is arranged inside the outer member 83 through a plurality of circumferential rows of rolling elements 88. A coil is disposed within the magnetic ring assembly 84. This magnetic ring assembly 84 is fixed to an inner peripheral surface of a ring-shaped mounting member 89 mounted on the outer member 83, while the multi-pole magnet assembly 85 is mounted on an outer peripheral surface of a ring-shaped mounting member 90 mounted on the inner member 82. The mounting member 90 is a member concurrently serving as a core metal for the multi-pole magnet assembly 85. The mounting member 89 on which the magnetic ring assembly 84 is fixed is provided with a wireless transmission device 87 for transmitting wireless the rotational speed detection signal, represented by the electric power output generated by the electric power generator 86, through a transmitting antenna of the wireless transmission device 87 to the outside of the wheel support bearing assembly in the form of a radio wave for use in anti-skid control performed by the automobile anti-skid braking system (ABS). The mounting member 90 referred to above is a member that defines a core metal for the multi-pole magnet assembly 85 and includes a portion that defines a slinger 90a cooperable with a sealing member 91. The outer member 83 is operatively coupled with a knuckle 92, while the inner member 82 is operatively coupled with an outer race 93 of a constant velocity universal joint.
However, with the rolling bearing assembly equipped with the electric power generator of the structure discussed above, since the mounting members 89 and 90 are mounted respectively on the outer and inner members 82 and 83 of the bearing assembly and the magnetic ring assembly 84 and the multi-pole magnet assembly 85 are in turn mounted on the mounting members 89 and 90, respectively, a relatively large number of components are required. Also, the magnetic ring assembly 84 is required to be incorporated in the mounting member 89 with no gap formed therebetween to avoid the possibility that the magnetic ring assembly 84 may separate from the mounting member 89 under the influence of vibrations, resulting in complicated assemblage. Also, in order to secure a gap between the magnetic ring assembly 84 and the multi-pole magnet assembly 85 confronting the magnetic ring assembly 84, the mounting members 89 and 90 need to be exactly aligned coaxially with each other. For this reason, the mounting members 89 and 90 have to be precisely machined, resulting in increase of the cost. Yet, since even in this example, the electric power generator 86 and the wireless transmission device 87 are positioned at respective locations separate from each other, the wheel support bearing assembly of the structure shown in and described with reference to FIG. 39 has problems similar to those involved in the wheel support bearing assembly of FIGS. 38A and 38B.
Also, in the wheel support bearing assembly of the structure discussed above, in view of the relation in position with a wheel and a tire housing, the inboard side is in an environment exposed to saline dirt and grits splashed from the ground surface and, therefore, for protection of the raceways within the bearing assembly and, also, the electric power generator 86, a reliable and firm sealing performance is required.
However, in the wheel support bearing assembly of the structure shown in and discussed with reference to FIG. 39, the sealing member 91 is interposed between the mounting members 89 and 90 and, therefore, no contact pressure would be secured in the sealing member 91 due to an error in positioning of the mounting members 89 and 90 relative to each other, resulting in a risk of incomplete sealing. For this reason, in order for the positioning error to be compensated for, the sealing member 91 must have an increased sectional surface area, but the increased sectional surface area cannot often be secured in the sealing member 91 in view of the relation in position thereof relative to the peripheral component parts such as the knuckle 92, the outer race 93 of the constant velocity universal joint and others. Also, in the face of a pressing demand for compactization of the wheel support bearing assembly, the space delimited between the knuckle 92 and the outer race 93 of the constant velocity universal joint is extremely small. Yet, in view of the presence of the peripheral component parts, the sectional surface area of the electric power generator 86 cannot be increased and, therefore, it is generally difficult to secure the electric power that can be generated.
If the sealing member 91 is disposed directly between the outer and inner members 83 and 82 such as found in the standard wheel support bearing assembly having no electric power generator incorporated therein, the sealing performance could be secured, but the electric power generator 86 would be positioned outside the sealing member, resulting in addition of one or more extra sealing member.
It is also suggested to dispose the slinger 90a, cooperable with the sealing member 91, on the outer race 93 of the constant velocity universal joint to thereby increase the space for installation of the electric power generator 86 and, also, the space for installation of the sealing member 91, but it is difficult to secure a sufficient space for installation of the electric power generator 86 after all. Depending on the size of the electric power generator 86 and that of the sealing member 91, the cup portion of the outer race 93 of the constant velocity universal joint would be incapable of securing a required wall thickness. Where the wireless transmission device 87 is employed, the space for installation thereof is additionally limited.